Solid composite propellants containing decaborane



United States Patent Ofiice 3,006,743 Patented Oct. 31,: 1961 3,006,743 SOLID COMPOSITE PROPELLANTS CONTAINING DECABORANE manufacturing a solid propellant having a specific impulse of about 260 or greater. Still another object of this invention is to provide a method of manufacturing a high energy rocket propellant comprising ammonium per- Homer Fox and John Keller Barflesvme Okla" 5 chlorate, decaborane, and abutadiene-methylvinylpyridine assignors to Phillips Petroleum Company, a corporation of Delaware No Drawing. Filed Jan. 3, 1956, Ser. No. 556,779 18 Claims. (Cl.52-.5)

This invention relates to solid propellants for rockets. In one aspect this invention relates to a high energy rocket propellant.

.method for manufacturing a high energy rocket propellant.

Solid propellants can be classified with respect to composition as double base type, single base type, and composite type. An example of a double base propellant is ballistite which comprises essentially nitroglycerine and nitrocellulosef Examples of single base propellants are nitrocellulose and trinitrotoluene. Composite type propellants are generally composed of an oxidizer, and a binder or fuel. They may contain other materials to improve fabrication or increase ballistic performance such as a burning rate catalyst.

Rocket propellants have achieved considerable commercial importance as well as military importance. Jet propulsion motors of the type in which the propellants of this invention are applicable can be employed to aid a heavily loaded plane in take off. Said motors can also be employed as an auxiliary to the conventional power plant when an extra surge of power is required. Said motors can also be employed to propel projectiles.

Recently there has been much interest in the development of high energy rocket propellants. Much effort is being expended to develop propellants having a specific impulse of about 260 or greater. With a high specific impulse propellant, a higher burn out velocity (the velocity of the rocket at the time all the propellant is consumed) can be attained than when using the same weight of a propellant having a lower specific impulse. Thus, the use of higher specific impulse propellants makes it possible to use less propellant, or to carry more payload. More payload is particularly important in military aircraft where the amount of armament carried by the aircraft could well be limited by the amount of fuel which it is necessary for the aircraft to carry.

We have discovered a new high energy propellant. We have found that by incorporating decaborane as a component of a composite rocket propellant we can obtain a propellant having a specific impulse of about 260 or greater. Thus, broadly speaking, our invention comprises a rocket propellant, and a method for making said propellant, which is comprised of an oxidizer, decaborane, and a suitable binder.

'Ihe term specific impulse as used herein is defined as the impulse derived when one pound of propellant is consumed.

An object of this invention is to provide an improved solid propellant for rockets. Another object of this invention is to provide a solid propellant having a specific impulse of about 260 or greater. Another object of this invention is to provide a high energy rocket propellant comprising ammonium perchlorate, decaborane, and a butadiene-methylvinylpyridine copolymer binder. Another object of this invention is to provide a method of admixture of a suitable oxidizer,

energy rocket propellant comprising an intimate a suitable binder, and

In another aspect thIS'ifiVfiHtifi$f%i estaa edecaborameui H Decaborane, B I-I exists at ordinary temperatures and pressures in the form of colorless crystals. It has a melting point of 99.7 C. and a boiling point of 213 C. In addition to its relatively high melting point, decaborane is stable and relatively inert, under the conditions of propellant fabrication, toward the other components of the propellant. The above-mentioned properties of decaborane render it particularly advantageous for use as a component of high energy propellants. Broadly speaking, the ratio of oxidizer to decaboraneby weight in our propellant can be within the range of 18/ l to 2/1; preferably said ratio is within the range of 8.5/1 to 4.5/1. On

there is provided a v the basis of the propellant composition as a whole, the

ingredients can be present in the following range: oxidizer, a major amount of from 60 to by weight; decaborane, a minor amount of 5 to 30% by weight; and binder, a minor amount of from 2 to 35% by weight.

While ammonium perchlorate, because of its low cost and ready availability, is our presently preferred oxidizer, other oxidizers can be employed in our propellant. For example, other oxidizers which can be employed include among others, hydrazine diperchlorate, nitrosyl-perchlorate, nitronium perchlorate, and potassium perchlorate.

A presently preferred binder material can be prepared from conjugated diene-vinylpyridine copolymers having Mooney values (ML-4) in the range between 15 and 30, an organic acid content not greater than 1.5 weight percent, a soap content not greater than 1 weight percent and an ash content not greater than 1.5 weight percent. Such copolymers are superior binders in solid propellant compositions. However other conjugated diene-vinylpyridine copolymers can also be used. In addition to the copolymer, the finished binder usually contains various compounding ingredients and sometimes contains a burning rate catalyst. It is generally preferred that carbon black be present in the binder compositions although the presence of carbon black is not essential to the production of satisfactory propellant compositions. The amount of carbon black in the copolymer can be in the range of 0 to 35 parts by weight per hundred parts of the copolymer. Propellants containing these conjugated diene-vinylpyridine copolymers as binders have better ballistic and mechanical properties than similar propellant compositions in which low Mooney conjugated dienestyrene copolymers are employed as binders.

The copolymers employed in this propellant compositions are prepared by emulsion polymerization at temperatures generally in the range between 0 and F. Recipes such as the iron pyrophosphate-hydroperoxide, either sugar-free or containing sugar, sulfoxylate and persulfate are applicable. In these recipes at least 5 parts by weight of emulsifler, and preferably 6 parts, are employed per hundred parts of monomer with as much as 9 parts being applicableJt is generally preferred that polymerization be continued to between 80 and 90percent conversion. However, polymers prepared from 50 percent to quantitative conversion are applicable. Polymerization is effected under conditions so as to yield polymers having a Mooney value (ML-4) in the range between 15 and 30. The electrolyte content in the polymerization system should be kept at a minimum and a surface active agent such as Daxad 11 (sodium salt of condensed alkylaryl sulfonic acid) is generally used. A more stable latex is obtained when operating in this manner than in the absence of Daxad 11. p

The presently preferred copolymer is prepared from a monomer charge to the polymerization zone which contains from 5 to 50 percent by weight of polymerizable heterocyclic nitrogen base and from 50 to 95 percent by weight of the conjugated diene.

The conjugated dienes employed are those containing from 4 to 8 carbon atoms per-molecule and include 1,3- butadiene, isoprene, 2-methyl-l,3-butadiene, 2,3-dimethyl- 1,3-butadiene, and the like. methoxy and ethoxy and cyano derivatives of these conjugated dienes, are also applicable. Thus, other dienes, such as phenylbutadiene, 2,3-dimethyl-1,3-hexadiene, 2- methoxy-S-ethylbutadiene, 2 ethoxy-3-ethyl-l,3-hexadiene, 2-cyano-l,3-butadiene, are also applicable in the polymeric binders of this invention.

, Instead of using-a single conjugated diene, a mixture of conjugated dienes can be employed. Thus a mixture of 1,3-butadiene and isoprene can be employed as the conjugated diene portion of the copolymer.

The polymeriza-ble heterocyclic nitrogen bases which are applicable for the production of the polymeric materials are those of the pyridine and quinoline series which are copolymerizable with a conjugated diene and contain one and only one mercially.

These heterocyclic nitrogen bases have the formula R n R a B R B where R is selected from. the group consisting of hy- 4 drogen, alkyl, vinyl, alphameth ylvinyl, alkoxy, halo, hydroxy, cyano, aryloxy, aryl, and combinations of these groups such as haloalkyl, alkylaryl, hydroxyaryl, and the like; one and only one of said groups 'being selected from e group consisting of vinyl and alpha-methylvinyl; and the total number of carbon atoms in the Various alkoxy, such as nuclear substituted groups being not greater than 12. Examples of such compounds are 2-vinylpyridine; 2- vinyl-S-ethylpyridine; 2-methyl-5-vinylpyridine; 4-vinylpyridine; 2,3,4-trimethyl-Swinylpyridine; 3,4,5,6-tetramethyl-Z-vinylpyridine; 3-ethyl-5-vinylpyridine; 2,6-diet-hyl-4-vinylpyridine; 2-isopropyl-4-nonyl-5-vinylpyridine; 2-methyl-5-undecyl-3-vinylpyridine; 2,4-dimethyl-5,6 dipentyl-3-vinylpridine; Z-decyl-S-(a1pha-methylvinyl)pyridine; 2-viny1-3-methyl- 5 ethylpyridine; 2-methoxy-4- chloro-6-vinylpyridine; 3-vinyl-5-ethoxypyridine; 2-vinyl- 4,5-dichloropyridine; 2-(alpha-methylvinyl)-4-hydroxy-6- cyanopyridine; 2-vinyl-4-phenoxy-5-methylpyridine; 2- cyano-S-(alpha-methylvinyl)pyridine; 3 vinyl-S-phenylpyridine; Z-(para-methyl-henyl) 3-vinyl-4-methylpyridine; 3-vinyl-5-(hydroxyphenyl)pyridine; 2-vinlquinoline; 2- vinyl-4-ethylquinoline; 3-vinyl-6,7-di-n-propylquinoline; 2- methyl-4-nonyl-G-vinylquinoline; 4(alpha-methylvinyl)-8- dodecylquinoline; 3-vinylisoquinoline; l,6dimethyl-3- vinylisoquinoline; 2-vinyl-4-benzylquinoline; 3-vinyl-5- chloroethylquinoline; 3-vinyl-5,G-dichloroisoquinoline; 2- vinyl-6-ethoxy-7-methylquinoline; 3-vinyl-6-hydroxymethylisoquinoline; and the like.

Methods for the preparation of the above described conjugated diene-heterocyclic nitrogen base copolymers are disclosed and claimed in copending application Serial No. 470,371, filed November 22, 1954, by R. S. Hanmer et al.

Another superior binder material is one prepared from a copolymer of a conjugated diene with a vinyl heterocyclic nitrogen base of the pyridine and quinoline series and a quaternizing agent. Quaternizing agents which can be used include, for example, methyl iodide, benzotrichloride, benzylchloride, diethyl-bromomalonate and ethyl alpha-chloroacetoacetate. These superior binder materials and the method of producing them are disclosed and claimed in copending application Serial No. 284,447, filed April 25, 1952, by W. B. Reynolds and J. E. Pritchard entitled Solid Rocket Propellant Compositions.

As mentioned above the finished binder usually contains various compounding ingredients and can contain a burning rate catalyst. Thus it will be understood that erein and in the claims, unless otherwise specified, the term binder, when employed in connection with a conjugated diene-heterocyclic nitrogen base copolymer, is employed generically and can include a burning rate catalyst, and various compounding ingredients.

Curing agents which can be used in vulcanizing or curing the copolymers, utilized in the propellant grains of this invention, include the well known curing agents used in the art such as vulcanizing agents, including sulfur and sulfur compounds such as tetramethylthiuram disulfide, tetraethylthiruam disulfide and the like; accelerators such as the condensation product of mercaptobenzothiazole and cyclohexylamine, mercaptobenzothiazole, benzothiazyl disulfide, dithiocarbamates, zinc oxide, stearic acid, and the like; antioxidants such as hydroquinone benzylether, phenyl-p-naphthylamine, and the like; and other materials such as stitfeners, plasticizers and fillers.

If carbon black is to be used in the binder composition, it is generally added as an aqueous slurry to the latex or alternatively carbon black can be milled directly into the dry polymer.

Commonly used combustion rate catalysts which can be-utilized in the propellant grains of our invention include metal ferrocyanides and ferricyanides. Ferric ferrocyanides, such as Prussian blue, Berlin blue, Hamburg blue, Chinese blue, Paris blue, Milori blue, soluble ferric ferrocyanide such as soluble Berlin or Prussian blue which contains potassium ferric ferrocyanide, and ferric ferrocyanide which has been treated with ammonia, are among the materials which can be used. Ferrous ferricyanide (Turnbulls blue) is also applicable. Milori blue is a pigment similar to Prussian blue but has a red tint and is prepared by the oxidation of a paste of potassium ferrocyanide and ferrous sulfate. Other metal compounds such as nickel"ancreepper ferreeyan des,anm1m nium dichromate, and ferric oxide (rouge) can also be utilized.

The binder used as a lant mixture can be any of the above referred to copending applications. binder component can also be a natural rubber.

Any of the above described binders can be employed in the practice of our invention. In addition, many plastic, resinous, and other rubbery materials are suitable binder materials for the propellant of our invention. Thus the invention is not to be limited to any particular binder. Examples of other suitable binders can be grouped as follows: asphalt and pitches including natural asphalts having a 170 F. softening point, air blown asphalts having a 270 F. softening point, mixtures of asphalt and synthetic or natural rubber, pitch having a 240 F. softening point, and mixture of pitch and rubber; epoxy resins, such as Araldite 502 and Epon 834; liquid polymers such 'as polybutadiene, polybutene, polyisobutylene, and Thiokol LP-3; polyethylenes; rubbers, both natural and synthetic, such as, butadiene-heterocyclic nitrogen base copolymers, butadiene-styrene copolymers, butyl rubber, ethyl acrylate-methylvinylpyridine copolymers, polybutadiene, and hydrogenated polybutadiene;

the copolymers disclosed in Said waxes, both natural and synthetic having a melting point within the range of ISO-300 F.; synthetic resins and plastics such as the various acrylic and polyvinyl resins; and nitro polymers such as polynitro methmethacrylate, nitro polybutadiene and polynitrovinyl alcohols..

High specific high solids loading. Therefore, in general, conventional blending or casting methods are not applicable to the manufacture of our high energy propellants. Thus, as an added feature of our invention, there is provided a method of manufacturing a high energy propellant compirsing an oxidizer, decaborane, and a binder.

In one method for the preparation of our propellants, the oxidizer and decaborane are first pulverized to about a 200 mesh. Said pulverized materials are then dry blended with the binder, and the dry blend is then comecmr n enthofou novel P P I-W impulse propellants inherently require 40 sulfur 6 EXAMPLE I A butadiene/2-methyl-S-vinylpyridine (MVP) copolymer was prepared by emulsion polymerization at 41 F. in accordance with the following recipe:

5 Parts by weight Water 180 Butadiene 90 2-methyl-5-vinylpyridine 1 e P etassrem fattg ac p 3 a 6 KOH 0.1

KCl 0.1

. Daxad 11 3 0.3

FeSO -7H O 0.278

Diisopropylbenzene hydroperoxide 0.214

Tert-dodecyl mercaptan 0.45

Booster recipe Water 10 K4Pg0q 0.165 FeSO -7H 0 0.139 Diisopropylbenzene hydroperoxide 0.107 Tert-dodecyl mercaptan 0.45

Inhibitor present, 0.0! wt. ercent tert-butylcatechol.

5 Potassium oflice synthetic ru her soap. 3 Sodium salt of condensed alkyl aryl sulfonic acid.

The ingredients in the booster recipe were added when 60 percent conversion was reached. The reaction was continued to .88 percent conversion (total reaction time, 25.5 hours). After stripping, the coagulated copolymer had a Mooney value (ML-4) of 23.

A binder component for a propellant is prepared by combining the following materials:

Parts by weight 00 9 /10 butadiene/ MVP copolymer 1 Furnace carbon ark 20 Flexol TOP 1 20 Benzotrichloride 6.6 1.75 Butyl eight 2 2 Zinc oxide 5 Aerosol OT 3 1 pression molded under a pressure within thesr mgemfiof.

5,000 to 15,000 pounds per square inch gauge, for a period of time within the range of 5 to 30 minutes, and at a temeprature within the range of 70 to 200 F. After removal from the mold, the propellant can be-cured or not cured depending upon the binder used and the final properties desired in the propellant. If it is desired to cure the propellant, said curing is usually carried out at a temperature within the range of 160 to 250 F. for a period of time within the range of 5 to 48 hours.

Another method for the manufacture of the propellants of our invention comprises dissolving the binder in a suitable solvent, normal heptane; cyclchexaae baaene acetone, etc., and then coating the finely divided dry blend of oxidizer and decaborane with the binder solu tion. Said coating is preferably carried out in a mixing vessel equipped with suitable agitation means. After the particles of oxidizer and decaborane have been sufiicient- 1y coated with me biadee eelation thehsolve t iLLB; i N

moved by evacuation of the mixing vessel, agitation being continued during said removal of the solvent. After removal of all the solvent has been accomplished, and suflicient mixing of the components has occurred, the blend is transferred to the compressica mel apparatu and molded as described above.

1 Tri-2ethylhexyl phosphate. Dithiocarbamate. Sodium dioctyl snlfosuccinate.

A group of propellant charges having varying amounts of ammonium perchlorate oxidizer, the above binder component and decarborane is then prepared by the dry blending procedure described above. Grains are proeeeed es morngssiommoldingm,Tabhe 1 given below lists the compositions of said propellants and the specific impulse obtained when each is tested in a rocket motor.

TABLE I I Composition Specific Impulse /10 (Isp), lb. NH C10 Bd/MVP Decaborane, torce-secJlb. percent wt. Copolymer, percent wt. mass percent wt.

'90.?! 5.6 r e e 5% 252 A second group of propellants is prepared using an ammonium perchlorate oxidizer component, and the above binder component. Table H given below lists the com- 1msitions of said propellants and the specific impulse obtained when each is tested in a rocket motor.

A sider configuration so as to of the rocket motor inwhich pellants. V rial is one of the above described'butadiene alkyl vinylout departing fromthe of anoxidizer component TABLE I1 O posit! 21 cm o Specific Impulse /10 (Isp Lb. M 010 Bd torce-SecJlb. percent wt. copolymer, mess percent wt.

' The advantage of using decaborane in our propellant n is evident from acomparison of the above Tables land 11. Our propellants can be formed intograins'of any dee they are to beused. Thus, our propellants can be formed into external burning grains, internal burning grains, and external-internalburning grains. Also, anysuitable type of restrictor material can be placedon any desired portion on the surfaces of our propellants so as to control the burning of said prc A presently preferredtype of restrictor matepyridine copolymer binder materials.

As will be evident to those skilled in the art, in view the above discussion and disclosure, various modifications of the invention can be made andcarried out withspirit or scope of said invention. We claim: 7 1. A propellant composition consistingessentially of an intimate admixture of from 60-90 percent by weight selected from'the group consisting of ammonium perchloratehexanitroethane, hydrazine perchlorate, hydrazine diperchlorate, nitrosyl-perand potassium perchlo" decarborane is chlorate, nitronium perchlorate, rate; from 2-35 percent by weight of a binder component selected from the group consisting ofrubbery polymers and copolymers,

claim 1 claim 1 claim 1 claim 1 claim 1- 7. A propellant composition according to claim 1 whirlein said binderconsists essentially of a rubbermateri i 8. A propellant composition according to claim 1 wherein said binder consists essentially of a copolymer diene containing from 4 to 8 carbonatoms per molecule with a substituted heterocyclic nitrogen base selected from the fit the combustion chamber I wherein said binder consists LB-butadiene and. Z-vinylpjm'dine. p 14. A propellant composition according to claim 1 i wherein said binder consists essentially of a group consisting of pyridine, quinoline, alkyl substituted pyridine, and alkyl substituted quinoline, wherein the total number of carbon atoms in the nuclearalkyl substituents is selected from the is not more than 12 and wherein R;

group consistingof hydrogen and a methyl radical.

9. A- propellant composition. according to claim 8 wherein said binder consists essentially of a conjugated diene-vinylpyridine copolymer.

10. A propellant composition according to claim 8 'wherein said binder consists essentially of a conjugated diene-vinylquinoline. copolymer. a

11. A propellant composition according to claim I wherein said binder consistsessentially of a butadienelower alkyl vinylpyridine copolymer;

12. A propellant composition according to claim 1 wherein said binder consists essentially of a copolymer of 1,3-butadieneand 2-methyl-5-vinylpyridine.

13. A propellantcomposition according to claim 1 essentially of a copolymer of 1,3butadiene and 2-ethyl-5-vinylpy'ridine. p p

15. A propellant composition according to. claim 2 whereinthe weight ratio of ammonium perchlorate and 7 within the range of 18/1 to "2/1.

16. A propellant composition according to claim 2 wherein the weight ratio of ammonium perchlorate to decarborane is within the range of 8.5/1 to 4.5/1.

17. A solid propellant charge according to claim 1 wherein said oxidizer is ammonium perchlorate and said binder consists essentially of a copolymer of 1,3-butadiene and a lower alkyl-vinylpyridine.

18. A solid propellant charge according to claim 1 wherein said oxidizer is ammonium perchlorate and said binder consists essentially of a copolymer of 1,3-butadiene and Z-methyl-S-vinylpyridine.

References Cited in the file of this patent Proell et al.: The Journal of Space Flight, volume 2, No. 1, January 1950, pages 4 and 5.

copolymer of I 

1. A PROPELLANT COMPOSITION CONSISTING ESSENTIALLY OF AN INTIMATE ADMIXTURE OF FROM 60-90 PERCENT BY WEIGHT OF AN OXIDIZER COMPONENT SELECTED FROM THE GROUP CONSISTING OF AMMONIUM PERCHLORATE, HEXANITROETHANE, HYDRAZINE PERCHLORATE, HYDRAZINE DIPERCHLORATE, NITROSYL-PERCHLORATE, NITRONIUM PERCHLORATE, AND POTASSIUM PERCHLORATE, FROM 2-35 PERCENT BY WEIGHT OF A BINDER COMPONENT SELECTED FROM THE GROUP CONSISTING OF RUBBERY POLYMERS AND COPOLYMERS, NATURAL AND SYNTHETIC RUBBER, ASPHALTS, WAXES, PITCHES, EPOXY RESINS, POLYETHYLENE, ACRYLIC AND POLYVINYL RESINS, AND NITRO POLYMERS, AND FROM 5-30 PER CENT BY WEIGHT OF DECABORANE. 